A lead-frame is a metal frame forming an extension line lead terminal with a die pad which is used for fixing a semiconductor pellet used in a plastic mold IC and a ceramics package IC. There is used for the metal frame, a lead-frame forming metal plate made of alloy mainly containing copper or copper-nickel as a material. In recent years, an element of an active metal series such as titanium and chromium has been added to the material as well. In any event, it is desired that the material used have good mechanical strength, high electric conductivity, high softening temperature, a coefficient of thermal expansion matching the coefficient of thermal expansion of a semiconductor pellet and a package material, secured flatness of a lead, small bending anisotropy, good heat releasing performance, and a low cost. A pattern is formed on the lead-frame forming metal plate by a punching out or by etching with an etchant. Punching can be carried out at a low cost and a precise pattern can be formed by the etching method.
In recent years, development in semiconductor and integrated circuit manufacturing accompanied with an increased demand for electronic parts using lead-frames has resulted in an increased requirement for producing lead-frame having uniform quality in large volume.
In manufacturing lead-frame, there has been used in the past, an alloy plate mainly containing, for example, copper or an alloy plate mainly containing copper-nickel, and in order to remove rust preventives applied on the alloy plate, the alloy plate was subjected in regular succession to a degrease treatment and an acid cleaning treatment. Then, a liquid resist was coated on the plate surface by a wheeler coating method. For example, a light-sensitive layer of a dry type, such as a negative type was deposited and dried to provide a light-sensitive material layer. After the light-sensitive layer was exposed through a prescribed etching pattern, it was then subjected to a developing treatment and any exposed parts of the light-sensitive layer were removed. Then, the alloy plate was dipped in an etchant to form a prescribed etching pattern on the alloy plate surface.
In order to produce a conventional lead-frame having such a pattern formed thereon while having uniform quality in large volume, many sheets of the alloy plates described above were purchased and a lot of these alloy plates were subjected in succession to a degrease treatment to remove rust preventives on the alloy plates and then subjected to an acid cleaning treatment in a batch treatment. Then, a light-sensitive material was coated on the alloy plates thus obtained, followed by drying, to manufacture many sheets of the lead-frame forming metal plates in large volume.
However, in the conventional manufacturing process described above for the lead-frame forming material, whereby a lot of the metal plates were subjected, in succession, to a degrease treatment, then to an acid cleaning treatment in a batch treatment, followed by coating a light-sensitive material on the respective degrease-treated and acid cleaning-treated plates thus obtained, followed by drying, foreign matter tends to get in between the metal plate and the light-sensitive layer, which can cause breaking of wire in the lead-frame thus obtained after forming a pattern. Accordingly, it has been difficult to manufacture lead frames in large volume while maintaining uniform quality.